[Tutorial] Building your own DIY E-Stim Stereo Device

[JakofClubs]

Hello all!

I'm continuing work on assembling my box, using lolo's V2 design. I couldn't get the 100v/10w transformer and got the Parts-Express 70v/10w used on other designs (330-040). I'm wondering about the transformer connections. Some use the 8 ohm and 0.62v leads and others, such as this, use 4 ohms and larger voltage - 10 volts on this one. Those are pretty large disparities, so any advice is appreciated. I've read these threads many times and an answer using technical electrical engineering discussion is beyond my knowledge.

Along those lines, I haven't received the 3.9 ohm resistor yet. Is the unit usable without that until those parts arrive?

Thanks - BH

On the transformers, it ends up being about the primary to secondary turn ratio, so various combinations could work. I'd recommend sticking to the 8 ohm and 0.62v leads. You want the 3.9 ohm resistor to make sure the amp always sees a minimum of 3.9 ohms. I wouldn't use it with out it.

[bobhill]

Hello all!

I'm continuing work on assembling my box, using lolo's V2 design. I couldn't get the 100v/10w transformer and got the Parts-Express 70v/10w used on other designs (330-040). I'm wondering about the transformer connections. Some use the 8 ohm and 0.62v leads and others, such as this, use 4 ohms and larger voltage - 10 volts on this one. Those are pretty large disparities, so any advice is appreciated. I've read these threads many times and an answer using technical electrical engineering discussion is beyond my knowledge.

Along those lines, I haven't received the 3.9 ohm resistor yet. Is the unit usable without that until those parts arrive?

Thanks - BH

On the transformers, it ends up being about the primary to secondary turn ratio, so various combinations could work. I'd recommend sticking to the 8 ohm and 0.62v leads. You want the 3.9 ohm resistor to make sure the amp always sees a minimum of 3.9 ohms. I wouldn't use it with out it.

I was offline for a while and just saw this - thank you!

[bobhill]

Ok, I was able to get everything together and working. More on that later.

EDIT: I used lolol2's V2 design, but with the 70w/10v transformer used in the other thread.

EDIT 2: It's a Class II AC Power Unit - with the double squares

US Parts list:
Project box: https://www.amazon.com/dp/B06XSMK61Q
AC Power unit: https://www.amazon.com/dp/B073QTNF9F (Mine is marked as Class II - double squares)
Amplifier: https://www.amazon.com/dp/B07TSKNCSV
Parts Express 70w/10v Transformer (x2): https://www.amazon.com/dp/B0002KRA1U
On/Off Switch (3PDT): https://www.amazon.com/dp/B07MTTVH3W
Tri-phase switch: https://www.amazon.com/dp/B07SVWYKG1
10k Pots and volume knobs: https://www.amazon.com/dp/B07DHKBGLG (Found these later and would have purchased them: https://www.amazon.com/dp/B082FCXJZ2)
50w/22 ohm resistor (x2): https://www.amazon.com/dp/B07FDZH85J
50w/3.9 ohm resistor (x2): https://www.amazon.com/dp/B07FF3GYWC (Longer lead time - I also found this on overstock.com available more quickly)
Power in jack: https://www.amazon.com/dp/B08CVF3QXL
Input jacks (RCA): https://www.amazon.com/dp/B08ZLQHGNS
Output jacks (4mm banana): https://www.amazon.com/dp/B091TDC1LM
Output plugs (4mm banana): Bought some like these at Home Depot (https://www.amazon.com/dp/B07RJ3NX5Y )
Lead wires (2mm TENS): https://www.amazon.com/dp/B075MS5L66 (cut off 3.5mm jack and attach banana plugs above. The lead wires are too thin and will come out pretty easy, so you will need to patch to a thicker wire – I plan to do this with some spare 18 AWG lamp power cord wire)
Input (from PC) cable: https://www.amazon.com/dp/B01D5H8KO2

Miscellaneous work stuff:
Wire: https://www.amazon.com/dp/B089D3T1JD (I bought 26 AWG, but would get 24 if I did it again – just a little easier to work with)
Soldering kit: https://www.amazon.com/dp/B07S61WT16 (This one is pretty basic and there are plenty similar ones on Amazon, but it worked fine. I bought flux and rosin core electrical solder at Home Depot.)
Helping hands: https://www.amazon.com/dp/B08DLGTZNZ (DON’T GET THIS ONE – I found the arms difficult to adjust, would get something with “wire” arms)
WAGO solderless connectors: https://www.amazon.com/dp/B07NKSHVF6 (DEFINITELY GET THESE!!!)
Solderless/Heat shrink connectors: https://www.amazon.com/dp/B089D79FQL (I haven’t used, but probably will – these are pretty cool)
Mini Heat Gun: https://www.amazon.com/dp/B07G4VMSHW (Very helpful)
Alligator clips (for testing): https://www.amazon.com/dp/B096S2JXYW (I got these later, should have purchased with other materials)
Multimeter (if you don’t have one, you will need for testing): https://www.amazon.com/dp/B01N9QW620

Notes:
Project box: It’s a tight fit, perhaps someone else will find a better one. Also, this box has a LOT of little pre-set screw posts on the bottom, so you will need some material as a base. I found a thick plastic yard sign at Home Depot that worked well and was thin enough to cut with scissors – barely.
Power in jacks: I used a 2.5mm three pin jack first and could not get power to the board. This 2.1mm two pin jack worked on first try. It’s tight with the power unit at first, but works easily now. (The power unit says either will work.)

[fl0w]

...
Power supply
IT IS VITAL THIS IS CLASS 2
...

For future reference and beginners like me, there seems to exist two standards confusingly named Class 2 and Class II.
I believe, please someone correct me if I'm wrong, that what's vital is that it is Class II, or at least that seems to be what's used by medical equipment anyways. Whether Class 2 is of importance or not I don't know...

https://www.cui.com/blog/class-2-vs-cla ... r-supplies

[harryc]

...
Power supply
IT IS VITAL THIS IS CLASS 2
...

For future reference and beginners like me, there seems to exist two standards confusingly named Class 2 and Class II.
I believe, please someone correct me if I'm wrong, that what's vital is that it is Class II, or at least that seems to be what's used by medical equipment anyways. Whether Class 2 is of importance or not I don't know...

https://www.cui.com/blog/class-2-vs-cla ... r-supplies

Have edited it now, apologies to any confusion it caused
I too was a complete beginner and had no idea there was a difference

[diglet]

I'm intending to build a stim box, but I have questions. After researching I landed on this schematic:



D1: TVS 1.5kE15CA
cap: bipolar 330uf (according to mantrid, this results in a cutoff of around 110 Hz)
Resistors: I think the worst-case power on R22 is 4.5W (very unrealistic, assuming 12V RMS with 12V PSU), so I choose a 5W resistor to save space. R3.9 is 50W
Conrad 100V transformer elma TT IZ1892 as recommended
amp: TPA3116D2 XH-M543 as recommended.
plan is to use separate switches for power/A/B and 3 pots (master, A, B). 3.5mm jack input. Maybe upgrade to an amp with Bluetooth later.


Questions:

• I'm surprised we need a transformer with this much iron. Is saturation a concern with smaller transformers?
• Some boxes have the 3-phase switch before the transformers, or the TVS diode and power switch after the transformers, what are the advantages/disadvantages of each?
• Some users have capacitors and resistors near the volume pots example here, iirc these turn the pot into log or reverse-log pots. Is this recommended? Is the volume range/sensitivity on the default build satisfactory? Do people use the pots on the stim box at all, or just volume control on the computer/xtoys?

[fl0w]

Some users have capacitors and resistors near the volume pots example here, iirc these turn the pot into log or reverse-log pots. Is this recommended? Is the volume range/sensitivity on the default build satisfactory? Do people use the pots on the stim box at all, or just volume control on the computer/xtoys?

I was wondering the same thing and found this on /r/estim wiki

Potentiometer mod: this mod adds a 10K ohm fixed resistor between the hot terminal and wiper of a 10K ohm linear-taper potentiometer to make adjustments less-sensitive to small knob rotation. To eliminate any interference that can be picked up by the audio-input cable, a 470 pF capacitor is added between wiper and amplifier's audio-input ground. For longer life, choose potentiometers with plastic or CERMET resistance elements.

[diglet]

I performed some calculations, assuming 40w max output power.


linear: normal 10k pot.
antilog: 10k pot + 10k loading resistor between + and wiper, as in MEGA schematic.
log: 10k pot + 1k loading resistor between - and wiper, as recommended for audio applications to approximate a log pot.

My guess is that if you stim mostly at low power, antilog is better as it gives more sensitivity in the lower range. If you stim mostly at high power, log is better as it gives more sensitivity in the higher range. This amp seems very powerful, which seems to favor the antilog setup. Will have to perform some "experiments" before making final decision...

[JakofClubs]

[*]I'm surprised we need a transformer with this much iron. Is saturation a concern with smaller transformers?

I believe the transformers were selected for their turn ratio and trial and error.

[bobross235]

Session 1 / X

I finally decided to start building one myself. As I'm a complete beginner I'll share all my thoughts, learnings and mistakes here. Maybe it'll help someone and/or encourage another beginner to try it. I'm trying to understand everything to minimize errors.

I bought this soldering iron:
https://smile.amazon.de/gp/product/B000 ... =UTF8&th=1
This box of shrink tubing for insulation:
https://smile.amazon.de/gp/product/B003 ... UTF8&psc=1
And this solder:
https://smile.amazon.de/Flussmittel-Kol ... hdGY&psc=1

I already made some mistakes when ordering :)
I misunderstood
"2x Chinch Input (red) (black) (white) - 6.07€"
and ordered two red, two black, two white! Looking at the picture of course it would have made sense to only order two in total.

Connecting two parts
I don't have any fancy clamps to help me soldering so I basically use a three step approach I saw on youtube:
1. Heat up the iron and put solder on the first part (eg. cable)
2. Heat up the iron and put solder on the second part (eg. cinch input connector)
3. Hold both parts together, heat up with iron and hope they stay together
It's a bit tricky but I'm making slow progress.

I pretty much use a shrinking tube to insulate everything after soldering. Result of first piece


Connecting three parts
I counted 9 times where three cables need to be connected. Here's what I mean:

The best way I found to do this is by just buying two times 5 of these wago connection clamps for three cables:
https://www.amazon.de/gp/product/B017KQ ... UTF8&psc=1

How do switches work
Probably most of you are laughing by now :D
But I didn't completely understand how to connect the switch with the 6 pins so I had a closer look at the idea behind switches.
Looking at the smaller switch with 3 pins first. It's an "on-on" switch.

See the little numbers 1,2,3? The switch is either connecting 2 and 1 or its connecting 2 and 3.

It works the same for the switch with 6 pins. The middle row is connected to the side where the "switch is switched to". All three pins in the middle are either connected to all three pins on the left side or to all three pins on the right side.

Connecting the AMP board
Before it arrived I had NO idea how to connect the board.

I was positively surprised when I found out a cable is provided. It looks like this:

It has this small connector on both sides. So my idea was to cut the cable in the middle and solder the white/red cable to the two POTS and connect the black cable to WAGO clamp. I was a bit surprised that the black cable was not insulated within the gray tube. It only insulated up to the black shrink tubing, inside the gray insulation it's blank metal. But it's still long enough to connect it, so should be fine.

Here's the end of my first session and my first question to the experts: The pre-existing cables from the AMP board connector are WAY thinner than the 0,5mm cable I bought. Is this a problem?

[lolol2]

Looks/sounds good so far.

The pre-existing cables from the AMP board connector are WAY thinner than the 0,5mm cable I bought. Is this a problem?

No problem, on the input site of the amp is no heavy load, so thin wires are okay.
Mixing thin wires with thick wires is also okay, all calculations have to be based on the thinest part of the wire.
But in this usecase the thin wire is totally fine.

[Electro]

The areas that need thicker wires would be everything from the amp output until it goes into the transformer, that wire should be the thickness of the transformer wire themselves or larger, which is not particularly thick wire.

[bobross235]

Thanks a lot @Electro & @lolol2

Session 2 / X
(almost 4 hours today):

Finished everything left of the AMP board first. Tried to understand a bit more about the parts. ChatGPT was a big help.

ChatGPT: Describe in easy terms, what a "..." is doing:

Potentiometer:
A potentiometer is a type of resistor that has a variable resistance. It consists of a resistive element with two fixed endpoints and a third adjustable endpoint called the wiper. The position of the wiper determines the resistance between the two fixed endpoints, allowing the resistance to be varied continuously over a range of values. Potentiometers are commonly used as adjustable voltage dividers, for adjusting the volume or brightness in electronic devices, and for calibrating sensors.
Amplifier board:
An amplifier board, or amp board, is a circuit board that contains the components and circuitry necessary to amplify a small electrical signal. Amplification is the process of increasing the strength or size of a signal, and amplifier boards are used in a variety of electronic devices to boost signals to a level that can be used by speakers, headphones, or other devices.
The basic components of an amp board include one or more amplifiers, power supply components, and input and output connectors. The amplifier takes an input signal and amplifies it using a power supply, typically a voltage or current source, to produce a larger output signal. The input and output connectors allow the amp board to be connected to other devices in a system, such as a microphone or speakers.
Amp boards can be found in a wide range of electronic devices, including audio systems, home theaters, musical instruments, and other types of electronic equipment. They are an essential component in many devices that require amplification of signals to produce sound or other types of output.
Transformer:
A transformer in electronics is a device that transfers electrical energy from one circuit to another through electromagnetic induction. It consists of a primary winding, a secondary winding, and a core made of ferromagnetic material. The transformer is used to change the voltage and current levels in electrical circuits, and to provide electrical isolation between circuits.

Power Supply
I ordered the Leicke power supply first but as feared the one I got didn't have a "phase II" symbol. I found this one with very similar specs:
https://www.amazon.de/dp/B0BF9T6X64?psc ... ct_details
Would be great if the experts could have a quick look.
It has the double square sign on the back. It also provides a connector to two single cables so I don't need the additional power connector I initially ordered. The combination of the sign on the back and the fact the provided connector only allows two cables lets me hope its phase II.
I also tried to understand what phase II means and why it's important and to my understanding it's a safety feature, "similar" like a ground wire is a safety feature. It's additional protection in case of electrical faults. It's an additional layer of protection in form of double insulation.

That's the small connector provided with the power supply:



I continued following the schematics and finished almost all soldering.

Triphase mode
I tried to understand the triphase switch, hoping this is correct:
Switch off -> black cables are not connected:
The current flows from red to black1 and from yellow to black2.

Switch on -> black cables are connected:
Triphase mode. The current flows from both red and yellow to ONE black port. Just one black ports needs to be connected to the triphase cable and it doesn't matter which one.

Case
The case from the list wasn't available anymore. I bought this one which is a bit bigger. Did you just use wood drills to drill the holes?
https://www.amazon.de/dp/B07NVK538F?ref ... tails&th=1

Next steps
Still waiting for the 3,9 OHM resistors to be delivered. This will be the last step of building the unit.
I have an old plain digital multimeter to start testing. Hopefully that's sufficient?
My strategy for testing would be quite simple:
1. Test if there's no current flowing between red&black and yellow&black with no sound input
2. Test if there's currrent flowing with sound input and post the numbers here to hear your feedback.
I'll also post some more pictures of the whole unit next time.

Thanks again for your great support!

[SunnyDay]

Thanks everybody in the thread for sharing all this useful information.

I just wanted to add a note to recommend using correctly graded component for powering your device, to prevent safety hazard .

That means making sure the power socket part itself, and the wires from power socket to the power switch and then to the amplifier board have proper specifications. (The switch itself normally has limits well above requirement.)

In this post (the legendary post from lolol2 which is the reason why I'm here), the power supply is 12V/10A or 24V/5A, but power socket part in the list is only rated to 60 VA which is twice below power supply requirement of 120 VA (12V x 10A or 24V x 5A = 120 VA).
Also wires in parts list are 0.5mm2 (or 20 AWG) which is normally rated 1.5 A only (see note below). I wouldn't use it to connect the power socket to the switch or amplifier. The 12V x 10A power supply that I own uses 16 AWG wire (according to the thin printing on the cable) to transmit power to the power jack, so in this case that seems the way to go.

In this other post from a different author the power supply is 12V/5A, but the wires in part list are 26 AWG which are rated 0.361 A. On Amazon the product description says 3A, but that seems very very suspicious. I wouldn't use such a thin wire in any case to transmit that amount of power. I wouldn't even use it at all in the whole device to be fair.

Please note that there are many tables on the web about wire size and current limit, but some of them seem to mistake limits of jacketed wire with limits of crude in-air wire, which don't perform the same heat dissipation. The chart I use is this one, which also has good explanations.

My recommendation would be:

• use the same wire size as the power supply for the power part of the device. If in doubt 16 AWG (1.31 mm2) would be a safe value since it can withstand 10A
• then using the same wire for the rest of the device would be the safest bet, but it can be difficult because of wire stiffness. Using 18 AWG (0.8 mm2) seems to be a good compromise and 20 AWG (0.5 mm2) seems still acceptable but I wouldn't go thinner
• be sure that the power socket you add (if the amplifier board doesn't have one) can support the amount of power provided by the supply, refer to maker specs

Btw by making these comments I don't mean to nitpick and the work done in this thread is awesome, it's just that having to deal with a fire hazard in the middle of a stim session is never the most pleasant thing to do

[RacerXxX]

I can't find a speco t7010 transformer near me, shipments too high to reach Europe.
it would cost me around 70/80€ including shipping.
what can i find similar?

PS. I see some have the lowest outputs at 0.5w and 0.25w, while others have the lowest at 0.625w, would both be fine?